From b00484d130552c871cde1ccb60bfa794502444d0 Mon Sep 17 00:00:00 2001
From: Peter Veenstra <qbix79@users.sourceforge.net>
Date: Tue, 12 Oct 2004 16:19:45 +0000
Subject: [PATCH] basic FXTRACT support

Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@2021
---
 src/fpu/fpu.cpp            |  5 ++++-
 src/fpu/fpu_instructions.h | 13 ++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/fpu/fpu.cpp b/src/fpu/fpu.cpp
index bce87f7e..0d5d154f 100644
--- a/src/fpu/fpu.cpp
+++ b/src/fpu/fpu.cpp
@@ -16,7 +16,7 @@
  *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  */
 
-/* $Id: fpu.cpp,v 1.22 2004-09-08 08:46:37 qbix79 Exp $ */
+/* $Id: fpu.cpp,v 1.23 2004-10-12 16:19:45 qbix79 Exp $ */
 
 #include "dosbox.h"
 #if C_FPU
@@ -354,6 +354,9 @@ void FPU_ESC1_Normal(Bitu rm) {
 		case 0x03:   /* FPATAN */
 			FPU_FPATAN();
 			break;
+		case 0x04:  /* FXTRACT */
+			FPU_FXTRACT();
+			break;
 		default:
 		LOG(LOG_FPU,LOG_WARN)("ESC 1:Unhandled group %X subfunction %X",group,sub);
 		break;
diff --git a/src/fpu/fpu_instructions.h b/src/fpu/fpu_instructions.h
index ff7dc091..a810cebd 100644
--- a/src/fpu/fpu_instructions.h
+++ b/src/fpu/fpu_instructions.h
@@ -16,7 +16,7 @@
  *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  */
 
-/* $Id: fpu_instructions.h,v 1.21 2004-09-09 18:36:50 qbix79 Exp $ */
+/* $Id: fpu_instructions.h,v 1.22 2004-10-12 16:19:45 qbix79 Exp $ */
 
 
 static void FPU_FINIT(void) {
@@ -392,3 +392,14 @@ static void FPU_FSTOR(PhysPt addr){
 	}
 }
 
+static void FPU_FXTRACT(void) {
+	// function stores real bias in st and 
+	// pushes the significant number onto the stack
+	// if double ever uses a different base please correct this function
+
+	FPU_Reg test = fpu.regs[TOP];
+	Bit64s exp80 =  test.ll&LONGTYPE(0x7ff0000000000000);
+	Bit64s exp80final = (exp80>>52) - BIAS64;
+	Real64 mant = test.d / (pow(2.0,static_cast<Real64>(exp80final)));
+	FPU_PUSH(mant); 
+}